Purification of phenylphenol from dibenzofuran by azeotropic distillation

ABSTRACT

Dibenzofuran is separated from a mixture with ortho- or paraphenylphenol, or a mixture thereof, by an azeotropic distillation utilizing an azeotropic agent which is a glycol, glycol monoalkyl ether, alkanolamine, or dialkylenetriamine having an appropriate boiling point.

United States Patent Seeburger et al.

[151 3,655,522 Apizll, 1972 [54] PURIFICATION OF PHENYLPHENOL FROMDIBENZOFURAN BY AZEOTROPIC DISTILLATION [72] Inventors: Harold 0.Seeburger; Lee H. Horsley, both of Midland, Mich.

The Dow Chemical Company, Midland, Mich.

[22] Filed: Nov. 9, 1970 [21] Appl. No.: 88,101

[ 73] Assignee:

[52] U.S. Cl ..203/59, 203/6491, 260/3462 M, 260/620 [51] Int. Cl...B0ld 3/36, C07c 39/12 [58] Field of Search ..203/59, 64, 91; 260/3462M, 260/620 Primary ExaminerWilbur L. Bascomb, Jr.

-Attorney--Griswold & Burdick, D. H. Thurston and Richard W. Hummer [57]ABSTRACT Dibenzofuran is separated from a mixture with orthoorparaphenylphenol, or a mixture thereof, by an azeotropic distillationutilizing an azeotropic agent which is a glycol, glycol monoalkyl ether,alkanolamine, or dialkylenetriamine having an appropriate boiling point.

6 Claims, N0 Drawings PURIFICATION OF PHENYLPHENOL FROM DIBENZOFURAN BYAZEOTROPIC DISTILLATION BACKGROUND OF THE INVENTION In the preparationof phenol, o-phenylphenol, and p-phenylphenol by the caustic hydrolysisof chlorobenzene, some dibenzofuran is formed. Separation of thedibenzofuran, with a boiling point of 288 C., from o-phenylphenol (bp275 C.) and/or p-phenylphenol (bp 305 C.) is difficult to achieve bysimple distillation since the respective boiling points are so closetogether, and the separation is cumbersome and relatively expensive toaccomplish by caustic extraction. These difficulties have led to asearch for a convenient and effective method of separating dibenzofuranfrom the phenylphenols.

SUMMARY OF THE INVENTION The essential and novel feature of the presentinvention is the separation of dibenzofuran from orthoorpara-phenylphenol, or a mixture thereof, by use of particular azeotropicagents. Thus, dibenzofuran is separated from a mixture with orthoorpara-phenylphenol, or a mixture thereof, by adding to the mixture ofthese compounds an azeotropic agent which is a lower alkylene glycol,lower alkylene glycol monoalkyl ether, alkanolamine, ordi-lower-alkylenetriamine of appropriate boiling point, and thenfractionally distilling the dibenzofuran azeotrope from the mixture thusformed under conditions whereby substantial thermal decomposition isavoided.

DETAILED DESCRIPTION Appropriate azeotropic agents have atmosphericboiling points within the range from about 238 C. to about 288 C.,

with those having atmospheric boiling points of about 240-26 C. beingpreferred.

Representative azeotropic agents are lower alkylene glycols where thealkylene groups are of two to four carbon atoms, such as diethyleneglycol, dibutylene glycol, triethylene glycol and tripropylene glycol;lower alkylene glycol monoalkyl ethers, wherein the alkyl radical isfrom one to four carbon atoms, such as triethylene glycol monomethylether, triethylene glycol mono-n-butyl ether, and tripropylene glycolmonomethyl ether; di-lower-alkylenetriamines, such asdipropylenetriamine; 1,2,3-butanetriol; and lower alkanolamines, whereinthe N-hydroxyalkyl substituent is from two to four carbon atoms, such asdiethanolamine, diisopropanolamine, and Z-aminoethylethanolamine.Particularly preferred agents are diethylene glycol, triethylene glycolmonomethyl ether, diisopropanolamine, and dipropylenetriamine.

After the azeotropic agent is added to the impure phenylphenol, thedistillation of the mixture is conducted at any pressure, the onlylimitation being that the distillation temperature should not be so highas to cause substantial thermal decomposition of the compounds.Subatmospheric pressures are preferable to avoid excessively hightemperatures.

The comparative concentrations of the phenylphenol(s) and dibenzofuranmay vary widely. Essentially, the mixture can be of any proportion.However, when a large amount of dibenzofuran is present, it may beadvantageous to conduct a preliminary simple distillation so as toconcentrate the phenylphenol(s) to about 95 weight percent or greater,and then use the azeotropic process to provide the more difficult finalpurification.

The quantity of azeotropic agent employed is preferably just sufficientto remove the impurity. Insufficient agent results in incompletepurification. Excess reagent does no harm except to require extra andunnecessary distillation to remove it. The amount of azeotropic agentrequired is dependent on the amount of dibenzofuran in the mixture, theazeotropic agent employed, the operating pressures of distillation, andthe apparatus used in the distillation. The optimum amount of azeotropicagent for a particular system is best determined by experience usingthese factors as a guide.

The process of the present invention is conveniently adapted to either abatch or preferably a continuous flow operation. In a continuous flowoperation, the crude phenylphenol(s)-dibenzofuran mixture is pumped intoa distillation column at an appropriate feed point dependent on itscomposition. Sufficient azeotropic agent is fed into the column tomaintain the agent in the upper two-thirds of the column length duringthe distillation. The dibenzofuran and azeotropic agent are collected asthe distillate, and the residue contains the phenylphenol(s).

Since many of the azeotropic agents of the present invention are atleast partially insoluble in the dibenzofuran, the distillate usuallywill form two phases. This phenomenon can be advantageously used in thecontinuous flow operation because this easy separation permitsconvenient return of the azeotropic agent layer to the distillation.

DESCRIPTION OF PREFERRED EMBODIMENTS 0 Example 1: Separation ofDibenzofuran from o-Phenylphenol A mixture containing 98 percent byweight of o-phenylphenol and 2 percent by weight of dibenzofuran wasdistilled by use of a 1 Vs X 30 distillation column packed with Aceramic Berl saddles equivalent to four to five theoretical plates. Aregulated reflux ratio of 5:1 was used and the pressure was maintainedat 50 mm. Hg absolute. 6.9 percent by weight of the total aromatics wasremoved by distillation, giving a residue which analyzed as 98.9 percentby weight of o-phenylphenol and 1.1 percent by weight of dibenzofuran.

The above distillation was repeated under identical conditions, exceptfor the addition of an azeotropic agent to theophenylphenol-dibenzofuran mixture in such amount as to give adistillation mixture which was 73.5 weight percent o-phenylphenol(o-PP), 1.5 weight percent dibenzofuran (DBF) and 25.0 weight percentazeotropic agent. Table 1 summarizes the azeotropic agents employed andthe composition of the residue as expressed in weight percent of totalaromatics exclusive of the excess azeotropic agent remaining.

Example 2: Separation of Dibenzofuran from p-Phenylphenol Distillationin the same manner as outlined in Example 1 of a mixture of 65.33 weightpercent of p-phenylphenol, 1.33 weight percent dibenzofuran, and 33.33weight percent of diethylene glycol gave a residue, after removal of 1.6weight percent of the aromatics, which was 100.0 weight percentpphenylphenol, exclusive of excess azeotropic agent remaining.

Example 3: Effect of Pressure on an Azeotropic System Distillations wererun on the same o-phenylphenoldibenzofuran-diethylene glycol mixtureused in Example 1 under identical distillation conditions except thatthe pressure was varied. The data are summarized in Table 2.

200 1.98 99.7 0.3 350 1.87 99.9 0.1 atmospheric 1.39 99.5 0.5

To remove dibenzofuran from a mixture of orthoand paraphenylphenol, theazeotropic agent is added and the distillation conducted in the manneroutlined in Example 1. The residue then is a mixture of the ortho andpara-isomers and any excess agent, and simple distillation separatesthese compounds.

When the azeotropic agent used in the foregoing examples is replaced bya similar amount of dibutylene glycol, triethylene glycol, tripropyleneglycol, triethylene glycol mono-n-butyl ether, tripropylene glycolmonomethyl ether, 1,2,3-butanetriol, diethanolamine, or-N-( 2-aminoethyl)ethanolamine and the mixture is distilled as shown above,dibenzofuran is separated from the phenylphenol with comparableefficiency.

We claim:

1. A method for separating dibenzofuran from a mixture witho-phenylphenol, p-phenylphenol, or a mixture of these phenols, whichcomprises adding to the mixture of the dibenzofuran and the phenylphenolan azeotropic agent selected from the group consisting of1,2,3-butanetriol, lower alkylene glycol, lower alkylene glycolmonoalkyl ether, dilower-alkylenetriamine, or lower alkanolamine, saidagent having an atmospheric boiling point within the range from about238 C. to about 288 C., and then fractionally distillingdibenzofuran-azeotropic agent azeotrope from the mixture thus formed.

2. The method of claim 1 wherein the azeotropic agent has a boilingpoint of about 240-260 C. at atmospheric pressure.

3. The process of claim 2 wherein the azeotropic agent is diethyleneglycol, triethylene glycol monomethyl ether, diisopropanolamine, ordipropylenetriamine.

4. The process of claim 3 wherein dibenzofuran is separated fromo-phenylphenol.

5. The process of claim 3 wherein dibenzofuran is separated fromp-phenylphenol.

6. The method of claim 1 wherein the fractional distillation isconducted at subatmospheric pressure.

2. The method of claim 1 wherein the azeotropic agent has a boilingpoint of about 240-260* C. at atmospheric pressure.
 3. The process ofclaim 2 wherein the azeotropic agent is diethylene glycol, triethyleneglycol monomethyl ether, diisopropanolamine, or dipropylenetriamine. 4.The process of claim 3 wherein dibenzofuran is separated fromo-phenylphenol.
 5. The process of claim 3 wherein dibenzofuran isseparated from p-phenylphenol.
 6. The method of claim 1 wherein thefractional distillation is conducted at subatmospheric pressure.